Method of and apparatus for utilizing and operating a hydrokinetic torque converter with lockup clutch

ABSTRACT

The power train of a motor vehicle employs a torque transmitting apparatus having a hydrokinetic torque converter with a lockup clutch and a torsional damper between the output member of the clutch and the hub of the turbine in the cover of the torque converter. The torque capacity of the damper is less than the nominal torque of the engine whose output element drives the cover of the torque converter. The lockup clutch is designed in such a way that the transmission of torque from the cover to the damper can be regulated in several stages, one of which involves the transmission of torque within a range of between about 10% and 60% of the maximum torque transmitted by the engine and another of which involves the transmission of torque corresponding to not less than 60% of the maximum torque transmitted by the engine.

CROSS-REFERENCE TO RELATED CASE

The disclosure of the patent application is a division Ser. No.08/306,671 now U.S. Pat. No. 5,752,894 filed Sep. 15, 1994 by RobertFischer for "Apparatus for utilizing and operating a hydrokinetic torqueconverter with lockup clutch" is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to improvements in methods of, and in apparatusfor, transmitting torque from a prime mover to one or more driven units,for example, for transmitting torque from a rotary output element (suchas a crankshaft or a camshaft) of the engine to one or more wheels of amotor vehicle. More particularly, the invention relates to improvementsin methods of, and in apparatus for, transmitting torque by way of ahydrokinetic torque converter which is equipped with a lockup clutch orbypass clutch. Still more particularly, the invention relates toimprovements in methods of, and in apparatus for, transmitting torque byway of a hydrokinetic torque converter which can transmit torque by wayof a turbine and/or by way of a slipping lockup clutch constructed andassembled to operate in parallel with the turbine. The invention alsorelates to a method of, and to means for, regulating the operation of aslipping lockup clutch for the purpose of ensuring that the magnitude oftorque which the clutch can transmit is a function of then prevailingoperating conditions.

In accordance with a presently preferred embodiment, the method of theinstant invention can be practiced to regulate the operation of anapparatus which can be installed in the power train of a motor vehicleto transmit torque between the output element of the engine and theinput element of an automatic transmission, and wherein the apparatusemploys (a) a hydrokinetic torque converter having a turbine and alockup clutch (such as a friction clutch) operating in parallel with theturbine, (b) means for monitoring one or more variable parameters andfor generating and memorizing corresponding signals, and (c) means (suchas a central computer or processor) for evaluating, processing andapplying the signals to regulate the slippage of, as well as thetransmission of, torque by the lockup clutch.

As a rule, a hydrokinetic torque converter which can be utilized in thenovel apparatus and/or in accordance with the novel method comprises apump, a turbine, a stator and a housing or cover which is driven by therotary output element of a prime mover (such as the engine of a motorvehicle) and transmits torque to the pump. The cover is coaxial with thepump and with the turbine and defines a chamber which accommodates theturbine as well as a lockup clutch. The lockup clutch can transmittorque from the cover directly to the turbine or to a part which isdriven by the turbine, and such clutch can constitute or include afriction clutch having a first friction surface on a substantiallyradially extending portion of the cover and a second friction surfaceprovided on a piston which is movable in the cover in the axialdirection of the turbine to move its friction surface into or away fromfrictional engagement with the first friction surface so that themagnitude of torque which the clutch can transmit depends on the extentof frictional engagement between the first and second surfaces. Thesecond friction surface is normally provided on a radially outer portionof the piston, and the radially inner portion of such piston cantransmit torque directly to the turbine or to a part (e.g., the rotaryinput element of a transmission which receives torque from the turbineor a hub which is of one piece with or is separably connected to theturbine and is also non-rotatably coupled to the input element) whichreceives torque from the turbine when the two friction surfaces of thelockup clutch are free to slide relative to each other.

Apparatus of the above-outlined character are disclosed, for example, inpublished German patent application No. 31 30 871, in U.S. Pat. No.5,029,087 and in U.S. Pat. No. 4,577,737.

It is also known to regulate the operation of the lockup clutch in aconventional hydrokinetic torque converter by selectively varying thepressure in an internal chamber of the torque converter or byselectively varying the pressure differential between bodies of fluid incompartments at opposite sides of the aforementioned piston. The purposeof such regulation is to select those stages or phases of operation ofthe apparatus when the lockup clutch is called upon to transmit torquedirectly from the cover (i.e., from the output element of the primemover) to the part or parts which are to receive torque from the turbinewhen the lockup clutch is not in use.

The aforementioned published German patent application No. 31 30 871discloses a method which includes monitoring the slippage between theinput and output members of the lockup clutch, comparing the thusascertained values with preselected values of slip, and adjusting theoperation of the lockup clutch when the monitored values depart from thepreselected values. The German patent application proposes to adjust theoperation of the lockup clutch by varying the pressure on a body offluid in a chamber at one side of the axially movable piston of thelockup clutch until the difference between the RPM of the input memberand the RPM of the output member of the clutch reaches a desired value,at least within a relatively low RPM range of the output element of theprime mover. In other words, the method which is proposed in thepublished German patent application is based on the well-known principleof regulating the slippage between the input and output members of thelockup clutch when the actual slippage departs from a predeterminedslippage.

The disclosure of the U.S. Pat. No. 5,029,087 is analogous to that ofthe aforediscussed published German patent application No. 31 30 871,i.e., the U.S. reference also discloses a method of monitoring theslippage of the lockup clutch in the cover of a hydrokinetic torqueconverter, comparing the thus ascertained slippage with preselectedvalues, and regulating the pressure of a body of fluid in a compartmentof the torque converter in a sense to eliminate the differences betweenthe actual slippage and the desired slippage of the lockup clutch. Thepatent further proposes to regulate the slippage of the lockup clutch inthe aforedescribed manner while the RPM of the output element of theprime mover is within a relatively low range of revolutions per minute.

The disclosure in the U.S. Pat. No. 4,577,737 is also analogous to thatof the published German patent application No. 31 30 871.

The proposals to regulate the operation of a lockup clutch in a manneras disclosed in the aforediscussed publications have met with limitedcommercial success or no commercial success at all. The reason for suchabsence of acceptance is believed to be that the aforementioned patentsand the aforementioned patent application propose to regulate theslippage of the input and output members of a lockup clutch relative toeach other while the RPM of the prime mover driving the cover of thehydrokinetic torque converter is relatively low, namely immediatelyabove the idling speed of the prime mover. If the prime mover is theengine of a motor vehicle, the vehicle is likely to be operated,primarily or even exclusively, in such a way that the RPM of the outputelement of the engine is within the aforementioned relatively low rangeof rotational speeds. This means that, due to slippage of the input andoutput members of the lockup clutch in order to prevent the transmissionof oscillations to the driven unit or units (such as an automatictransmission), the energy requirements (i.e., the fuel consumption) ofthe motor vehicle are increased accordingly. Furthermore, the slippagewhich is to take place while the RPM of the output element of the engineis relatively low (i.e., immediately or closely above the idling RPM)cannot be selected at will or with a requisite degree of accuracybecause the operating parameters and operating conditions whichrespectively develop and take place at such low RPM of the outputelement of the engine cannot be relied upon to select the fluid pressurewhich is necessary to effect a slippage-free engagement of the lockupclutch. One of the reasons is that the pressure of fluid in the cover ofthe torque converter is low when the transmitted torque is relativelysmall and such low pressure of fluid cannot be regulated with the degreeof accuracy which is needed to ensure that the slippage of the input andoutput members of the lockup clutch will vary with a degree ofpredictability which is needed to guarantee that the magnitude of torquebeing transmitted from the output element of the engine to one or moredriven units in the power train of a motor vehicle will correspond tooptimum torque for the prevailing operating conditions. It has beenascertained that, since the pressure of the fluid in the cover of thetorque converter is relatively low when the magnitude if the transmittedtorque is small, even minor fluctuations of fluid pressure are likely toentail pronounced variations of slippage between the driving and drivenmembers of the lockup clutch. Furthermore, it is necessary to take intoconsideration the hysteresis of the valve or valves which are utilizedin such torque converters to regulate the pressure of the fluid in theinterior of the cover (e.g., the friction between the cylinder and thepiston of a valve which forms part of the controls for the torqueconverter), and such hysteresis renders it necessary to maintain acertain level of fluid pressure in order to account for the hysteresis.Otherwise stated, the accuracy of regulation of the torque which isbeing transmitted by the lockup clutch in conventional hydrokinetictorque converters decreases in response to a reduction of the magnitudeof torque to be transmitted from a prime mover to one or more drivenunits, e.g., from the combustion engine to the transmission in a motorvehicle.

Another drawback of heretofore known proposals to regulate the operationof a lockup clutch or bypass clutch in a hydrokinetic torque converteris that, when the RPM of the output element of the engine is relativelylow and the load upon the power train of the vehicle is also low (thistakes place quite frequently when the RPM of the output element of theengine is not much higher than the idling RPM), low-amplitudefluctuations of transmitted torque often result in short-lastingadherence to one another of abutting friction surfaces of the input andoutput members of the lockup clutch at a time when the lockup clutch issupposed to slip. The intervals of adherence alternate with intervals ofslippage, and such alternating slippage and adherence entail thegeneration of pronounced rattling and buzzing noises in the power trainof a motor vehicle. Moreover, alternating intervals of adherence andslippage often initiate abrupt changes of the torque which is beingtransmitted to the input element of a transmission in the power train ofa motor vehicle. The only heretofore known solution for such problems isto increase the slippage between the input and output members of thelockup clutch which, in turn, entails highly increased energyrequirements for the engine.

Still another drawback of heretofore known proposals to regulate theslippage of a lockup clutch in a hydrokinetic torque converter in thepower train between the prime mover and the transmission of a motorvehicle is that, when the RPM of the output element is relatively low(e.g., within a range immediately above the idling RPM), i.e., when thepower train is under a mere partial load, the torque which is to betransmitted from the lockup clutch to the driven input element of atransmission or another driven unit of the motor vehicle can be reducedto the required value only with a considerable outlay for regulatingequipment. The reason is that the magnitude of the torque to betransmitted under such circumstances is not dependent solely upon theclutch engaging force but also depends on the characteristics of thefriction surfaces of the input and output members of the lockup clutch.Such characteristics of the friction surfaces, in turn, are a functionof a number of different parameters including the temperature of theinput and/or the output member, the RPM at which the friction surfacesare to slip relative to one another, the characteristics of the fluid(e.g., oil) in the cover of the hydrokinetic torque converter and/orcertain other factors. Therefore, the characteristics of the frictionsurfaces are likely to fluctuate within a very wide range and,consequently, the means for regulating the slippage must be designed totake into consideration and to compensate for the influence of at leastsome if not all of the above-enumerated parameters. This is proposed tobe accomplished by selecting a relatively high RPM at which the frictionsurfaces of the input and output members of the lockup clutch begin toslip relative to each other, namely to adhere to a relatively highminimum RPM at which the lockup clutch begins to slip. This is intendedto ensure that the RPM at which the lockup clutch will begin to slip issufficiently high to prevent the transmission of fluctuations of torqueof the output element of the prime mover to the input element orelements of one or more units receiving torque from the turbine of thehydrokinetic torque converter or from the lockup clutch.

OBJECTS OF THE INVENTION

An object of the invention is to provide a hydrokinetic torque converterand a lockup clutch or bypass clutch which can be utilized in or withsuch torque converter to overcome the above-enumerated drawbacks ofconventional hydrokinetic torque converters.

Another object of the invention is to provide a torque transmittingapparatus which embodies a hydrokinetic torque converter and a lockupclutch and which is constructed and assembled in such a way that it canreliably prevent the transmission of oscillations of torque from theoutput element of a prime mover to the input element or elements of oneor more torque receiving units, for example, from the crankshaft orcamshaft of a combustion engine or other engine to the input element ofa transmission in the power train of a motor vehicle.

A further object of the invention is to provide a relatively simple,compact and inexpensive lockup clutch which can be utilized in or withthe hydrokinetic torque converter in an apparatus of the above-outlinedcharacter.

An additional object of the invention is to provide a lockup clutchwhich can reliably and highly satisfactorily damp the fluctuations oftorque which are being transmitted from a prime mover to the inputmember of the lockup clutch and from the output member of the lockupclutch to one or more driven units, e.g., to a transmission in the powertrain between the prime mover and one or more wheels of a motor vehicle,within the entire RPM range of the output element of the prime mover.

Still another object of the invention is to provide an apparatus whichexhibits the above-enumerated features and advantages and which rendersit possible to transmit torque from a prime mover to one or more drivenunits with considerable savings in energy requirements for the primemover.

A further object of the invention is to provide a novel and improvedmethod of transmitting torque from a prime mover to one or more drivenunits with hydrokinetic torque converter and a lockup clutch or bypassclutch which is utilized with or forms part of the torque converter.

Another object of the invention is to provide a novel and improvedmethod of regulating the slippage of a lockup clutch or bypass clutch inthe cover of a hydrokinetic torque converter.

An additional object of the invention is to provide a novel and improvedsystem for regulating the operation of a lockup clutch in a hydrokinetictorque converter which is installed in the power train between the primemover and one or more wheels of a motor vehicle.

Still another object of the invention is to provide a power train whichembodies the above-outlined torque transmitting apparatus.

A further object of the invention is to provide a motor vehicle whichembodies the above-outlined powertrain with a hydrodynamic torqueconverter and a lockup clutch.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of anapparatus for transmitting torque from a rotary output element of aprime mover, such as an internal combustion engine in a motor vehicle.The improved apparatus comprises a hydrokinetic torque converterincluding a slipping lockup clutch or bypass clutch having orcooperating with a torsion damper whose torque capacity (i.e., themaximum torque which the damper can transmit) is less than the nominal(i.e., maximum achievable) torque of the prime mover.

The torque capacity of the damper can be between about 10% and 60%(preferably between about 25% and 50%) of the nominal torque of theprime mover.

The damper is or can be constructed and assembled in such a way that itis devoid of discrete friction generating means. For example, the dampercan be constructed and assembled in such a way that it comprises rotaryinput and output members which are turnable relative to each otherthrough an angle of between about ±2°, and ±8°, preferably between about±3° and ±6°.

The damper can be designed with a view to ensure that its rigidity isbetween about 7 Nm/° and 30 Nm/°.

Another feature of the invention resides in the provision of a method oftransmitting torque by a slipping lockup clutch or bypass clutch in ahydrokinetic torque converter which transmits torque to a transmissionhaving at least one forward shift stage or speed ratio. The improvedmethod comprises the step of regulating the transmission of torque bythe lockup clutch as a function of variations of energy- and/orpower-related-parameters at least in the at least one forward shiftstage or speed ratio of the transmission.

A further feature of the invention resides in the provision of a methodof transmitting torque by a slipping lockup clutch or bypass clutch in ahydrokinetic torque converter which receives torque from an engine, suchas an internal combustion engine in a motor vehicle. The methodcomprises the step of regulating the transmission of torque by thelockup clutch in two stages, one of which involves the transmission oftorque within a range of between about 10% and 60% (preferably within arange of between about 15% and 50%) of a maximum torque beingtransmitted by the engine. The other stage involves the transmission oftorque corresponding to not less than about 60% of the maximum torquetransmitted by the engine.

The magnitude of torque which the clutch can transmit during the onestage can exceed the magnitude of torque being actually transmitted bythe engine. For example, the magnitude of torque which the lockup clutchtransmits during the one stage can be between 1 and at least 1.2 timesthe magnitude of torque being simultaneously transmitted by the engine.

An additional feature of the invention resides in the provision of anapparatus for transmitting torque from a rotary output element of anengine (e.g., the crankshaft or the camshaft of an internal combustionengine in a motor vehicle). The apparatus comprises a hydrokinetictorque converter including a slipping lockup clutch or bypass clutch anda torsional damper which is arranged to take up fluctuations (if any) oftorque within a first range of torques transmitted by the output elementof the engine. The lockup clutch is designed and is operative to slip inresponse to fluctuations of torque within a second range of torqueswhich are being or which can be transmitted by the output element of theengine. Such apparatus can further comprise means for reducing themagnitude of torques which the damper can transmit within the firstrange of torques in response to pronounced oscillations of torque beingtransmitted by a power train which includes the torque converter. Themeans for reducing the magnitude torques can be constructed, assembledand operated to be responsive to resonance RPM and/or to changes of loadupon the engine.

Still another feature of the invention resides in the provision of anapparatus for transmitting torque from a rotary output element of anengine. The apparatus comprises a hydrokinetic torque converterincluding a turbine, a slipping lockup clutch or bypass clutch having aninput member receiving torque from the output element of the engine(e.g., by way of a cover or housing of the torque converter), and atorsional damper between an output member of the lockup clutch and theturbine. The damper has a torque capacity at least approximating anupper limit of a first range of a plurality of ranges of torque beingtransmittable by the engine. The minimum torque which can be transmittedby the lockup clutch at least within a portion of the first range oftorques transmittable by the engine can equal or exceed 1% of thenominal torque of the engine. The lockup clutch can be designed in sucha way that the torque which the clutch can transmit at least during aportion of the first range of torques transmittable by the engine is atleast substantially constant.

At least the major part of the first range of torques transmittable bythe engine is or can be transmitted within a main driving or operatingrange of the engine, namely a range of operations most frequentlyresorted to when the engine is in use, e.g., to drive the wheels of amotor vehicle. The major part of the first range of torquestransmittable by the engine can be within a portion of the main drivingrange of the engine which encompasses at least one of an FTP75 cycle,i.e., U.S. Federal Test Procedure 75, and an ECE cycle, i.e. EuropeanCommunity Exhaust Testing Procedure, for urban traffic at a speed of 90km/h and highway traffic at a speed of 120 km/h, it being assumed herethat the engine is installed in a motor vehicle.

The first range of torques can be selected in such a way that it isbeing transmitted while the engine is driven within an engine RPM rangeof between idling RPM and about 3000 RPM, preferably between idling RPMand 2000-2500 RPM.

The aforementioned plurality of ranges further embraces a second rangeof torques transmittable by the engine. The torque transmitting capacityof the lockup clutch within the second RPM range of the engine can bebetween about 0.6 and 0.99 times (preferably between about 0.8 and 0.9times) the actual torque being transmitted by the output element of theengine.

A further feature of the invention resides in the provision of anapparatus for transmitting torque from a rotary output element of anengine in a motor vehicle to a rotary input element of a variable-speedtransmission having a plurality of speed ratios. The apparatus comprisesa hydrokinetic torque converter including an engageable anddisengageable lockup clutch, and means for monitoring the speed of themotor vehicle to ascertain whether or not a disengagement of the lockupclutch at a particular speed contributes to an increase of the towing orpulling force of the vehicle by way of the torque converter without achange in the speed ratio of the variable-speed transmission, todisengage the lockup clutch when such disengagement contributes to anincrease of the towing or pulling force, and to shift the variable-speedtransmission into a lower speed ratio when the disengagement of theclutch does not contribute to an increase of the towing or pullingforce.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved torque transmitting apparatus itself, however, both as to itsconstruction and the methods of using and operating the same, togetherwith additional features and advantages thereof, will be best understoodupon review of the following detailed description of certain presentlypreferred specific embodiments with reference to the accompanyingdrawings, wherein:

FIG. 1 is a fragmentary schematic partly elevational and partly axialsectional view of a torque transmitting apparatus employing ahydrokinetic torque converter and a lockup clutch which embody one formof the present invention;

FIG. 2 is a diagram showing the mode of transmitting torque in part byway of the hydrokinetic torque converter and in part by way of thelockup clutch of the apparatus which is shown in FIG. 1;

FIG. 3 is an axial sectional view of a specific embodiment of a torquetransmitting apparatus which embodies the present invention and whereinthe lockup clutch transmits torque to the turbine of the hydrokinetictorque converter by way of a novel and improved torsional damper;

FIG. 4 is an elevational exploded view of the input member of the damperwhich is shown in FIG. 3;

FIG. 5 is an elevational view of the output member of the damper whichis shown in FIG. 3;

FIG. 6 is a diagram showing the characteristic curve of a multi-stagedamper which can be utilized in the improved torque transmittingapparatus;

FIG. 7 is a diagram showing the range of operation of the lockup clutchwith slip and the main driving or operational range of a conveyance inwhich the slip clutch is put to use;

FIG. 8 is a fragmentary elevational view of a modified torsional damperwhich can be utilized in combination with a lockup clutch in ahydrokinetic torque converter forming part of a torque transmittingapparatus which embodies the present invention;

FIG. 9 is a sectional view substantially as seen in the direction ofarrows from the line IX--IX of FIG. 8; and

FIG. 10 is a block diagram of a hydrokinetic torque converter, a lockupclutch and a computer for controlling them and the gear setting of anautomatic transmission driven by the converter and clutch.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a torque transmitting apparatus 10 which comprises ahydrokinetic torque converter 11 having a lockup clutch or bypass clutch12 which is operated by a pressurized fluid, such as oil. The clutch 12is a friction clutch which operates in parallel with the turbine 18 ofthe torque converter 11. The cover or housing 16 of the torque converter11 receives torque from the rotary output element 13 of a prime mover(not shown), such as the combustion engine of a motor vehicle. Theoutput element of the torque converter 1 1 is shown at 14; this elementcan constitute a hub of the turbine 18 and can be provided withcustomary axially parallel internal splines and teeth mating withcomplementary external teeth and splines of a rotary input element 14a,e.g., the input shaft of a transmission in the power train between theengine (i.e., output element 13) and one or more wheels of a motorvehicle. The transmission including the shaft 14a can constitute anautomatic variable-speed transmission having an output element arrangedto transmit torque to an axle of the vehicle.

In addition to the housing 16 and the turbine 18, the torque converter11 of FIG. 1 further comprises an impeller or pump 17 and a stator 19.The pump 17 receives torque from the cover 16 which, in turn, receivestorque from the output element 13 of the prime mover. The stator 19 islocated in the chamber of the cover 16 between the turbine 18 and thepump 17.

The lockup clutch or bypass clutch 12 which is shown in FIG. 1 is afriction clutch having a disc 20 with a friction surface 21 whichconfronts a second friction surface 22 on the adjacent radiallyextending portion of the cover 16. That portion (20a) of the disc 20which is provided with the friction surface 21 constitutes a pistonwhich is movable in the direction of the common axis X--X of the outputelement 13, turbine 18, cover 16, pump 17, output member or hub 14 andinput shaft 14a. The piston 20a divides the internal chamber of thecover 16 into two compartments 24 and 25 located at opposite sides ofthe disc 20. The apparatus 10 further comprises a torsion damper 20bwhich is installed between the piston 20a (i.e., the disc 20) and theoutput member or hub 14. When the clutch 12 is engaged so that ittransmits torque from the cover 16 directly to the hub 14, it operatesin parallel with the torque converter 11 proper, i.e., with the turbine18 in the chamber of the cover 16.

The torque converter 11 receives pressurized fluid from a source 30a(e.g., a pump) by way of a conduit 30 which discharges the fluid intothe chamber of the cover 16 and more particularly into that portion ofsuch chamber which is adjacent the pump 17. The means for regulating thepressure of fluid entering the conduit 30 includes a pressure regulatingvalve 31. The operation of the valve 31 is controlled by a regulatingunit 32 (e.g., a proportional action valve or a pulse width modulatedvalve) which, in turn, is controlled by a computer 32a, e.g., amicroprocessor (hereinafter called processor for short). The processor32a regulates the operation of the valve 32 depending upon a pluralityof variable parameters as well as characteristic curves stored in thememory of the processor 32a. The heated fluid which leaves the chamberof the cover 16 is caused to pass through a heat exchanger 33, and thethus cooled fluid can reenter the source 30a.

In addition to acting upon the turbine 18, the pressurized fluidentering the chamber of the cover 16 through the conduit 30 flows fromthe output side of the pump 17 into the compartment 24 at the right-handside of the piston 20a (as viewed in FIG. 1). Pressurized fluid in thecompartment 24 causes the piston 20a to move its friction surface 21into engagement with the friction surface 22 of the adjacent radiallyextending portion of the cover 16.

In accordance with a feature of the invention, the clutch 12 is causedto slip at least during certain stages of operation of the torquetransmitting apparatus 10. To this end, the pressure in the left-handcompartment 25 in the cover 16 of FIG. 1 is regulated by the valve 31which is connected with the compartment 25 by a conduit 34. The valve 31regulates the pressure of fluid in the compartment 25 in such a way thatit determines the differential between the pressures of the fluid in thecompartments 24 and 25 to thus determine the magnitude of torque whichis being transmitted by the lockup clutch 12.

Since the lockup clutch 12 is installed to transmit torque in parallelwith the turbine 18 of the torque converter 11, the torque (M_(PM))which is being transmitted by the prime mover equals the sum of torques(M_(C) and M_(P)) respectively transmitted by the clutch 12 and the pump17. Furthermore, and if one disregards the losses developed in the powertrain, the torque (MT) which is being transmitted to the input element14a of the transmission equals the sum of M_(C) and M_(TU) (the latterbeing the torque which is being transmitted by the turbine 18).Otherwise stated, M_(T) =M_(C) +M_(TU) or M_(C) +M_(P) times conversion.

FIG. 1 further shows that the valve 31 includes a port which isconnected to a tank 31a, that the connection between the source 30a andthe valve 31 comprises a check valve 30b and that the processor 32acomprises inputs connected to devices which generate signals denotingthe position of the valving element of the throttle valve in a motorvehicle, the RPM of the turbine, the RPM of the pump, the load upon theengine, the setting of the transmission including the input shaft 14a,the temperature of fluid in the chamber of the cover 16, one or moreother parameters of the torque transmitting system, and the conditionand/or other parameters of one or more auxiliary units.

FIG. 2 is a diagram showing the relationship of the torque M to theslippage (Δn) of the lockup clutch 12. It will be seen that themagnitude of the torque which is transmitted by the turbine 18 to thehub 14 increases when the slippage of the lockup clutch 12 increases. Inaccordance with one feature of the method of the present invention, theslippage of the clutch 12 is not regulated directly when slippage isdesired. Instead, the slippage is regulated depending on the operatingcondition of the prime mover, including or driving the rotary outputelement 13. The condition of the prime mover is monitored by at leastone signal generating device which, in turn, transmits signals to thecorresponding input of the processor 32a so that the latter induces thevalve 31 to select a desired differential between the pressures offluids in the compartments 24 and 25 within the cover 16. The desiredslippage between the surfaces 21, 22 of the lockup clutch 12 isthereupon determined automatically, i.e., without manual adjustment ofthe valve 31.

The torque transmitting apparatus 110 of FIG. 3 comprises a hydrokinetictorque converter 1 11 with a lockup clutch 112 and a damper 135 which isinstalled between the clutch 112 and the hub 114 of the turbine 118forming part of the torque converter 111. The torque converter 111further comprises a cover 116 which is driven by the engine of a motorvehicle by way of fasteners 116a and drives the impeller or pump 117.The stator 119 of the torque converter 111 is installed between the pump117 and the turbine 118. The fasteners 116a (only one shown in FIG. 3)serve to secure the cover 116 of the torque converter 111 to a disc (notshown) on the rotary output element (e.g., a crankshaft or a camshaft)of the combustion engine.

The lockup clutch 112 of FIG. 3 comprises an annular piston 136 whoseaxis coincides with the axis X--X of the torque converter 111 and whichis installed between the cover 116 and the turbine 118. The piston 136is or can be made of metallic sheet material, and its radially innerportion is non-rotatably but axially movably mounted on the hub 114 ofthe turbine 118. The radially outer portion of the piston 136constitutes a conical frustum and is provided with a friction lining 121having an exposed friction surface confronting the friction surface 122of the adjacent frustoconical portion of the cover 116.

The piston 136 is disposed between a compartment 124 and a compartment125 forming part of the chamber of the cover 116. The compartment 124 isdisposed between the piston 136 and the turbine 118, and the compartment125 is disposed between the piston and the cover 116. The means forchanging the axial position of the piston 136 includes means for varyingthe pressure of fluid in the compartment 125, namely for varying thedifferential between the pressures of the fluids in the compartments 124and 125. The magnitude of the torque M_(C) which is being transmitted bythe lockup clutch 112 is a function of such pressure differential.

The construction and mounting of the damper 135 are such that the torquecapacity or stop pin torque of the damper is less than the nominaltorque of the combustion engine which drives the cover 116. In otherwords, the damper 135 begins to act not unlike a solid body when themagnitude of the torque transmitted by the lockup clutch 112 is stillless than the maximum torque which the engine can transmit to the cover116 of the torque converter 111. Stated in still another way, the inputmember 138 of the damper 135 ceases to move relative to the flange-likeoutput member 139 of the damper before the magnitude of the torqueM_(PM) which is being transmitted to the cover 116 by the combustionengine of the vehicle in which the torque transmitting apparatus isinstalled reaches a maximum value. This can be achieved in a number ofdifferent ways. For example, the convolutions of the coil springs 137forming part of the damper 135 can be caused to fully abut each other sothat the springs 137 act not unlike one-piece solid bodies, or the inputand output members 138, 139 of the damper 135 can be provided with stopswhich come into abutment with each other before the magnitude of thetorque M_(PM) being transmitted to the cover 116 reaches a maximumvalue. The input member 138 of the damper 135 is non-rotatably securedto the piston 136, and the output member 139 of the damper 135 isnon-rotatably but axially movably coupled to the hub 1 14 of the turbine118. To this end, the output member 139 is provided with a set ofinternal axially parallel teeth mating with complementary axiallyparallel external teeth of the hub 114.

FIGS. 4 and 5 illustrate the details of a damper 135 which can beutilized in combination with the lockup clutch 1 12. The input member138 of the damper 135 comprises a plurality of segment-shaped sections140, namely a first pair of sections 140 which confront each other atone side of the axis X--X and a second pair of sections 140 confrontingeach other at the other side of the axis X--X diametrically opposite thesections 140 of the first pair. The sections 140 of each pair ofsections are affixed to the piston 136 by one or more rivets 141 and/orother suitable fasteners.

FIG. 5 shows the flange-like output member 139 of the damper 135. Thisoutput member comprises an annular main portion 139a which carries tworadially outwardly extending arms 142 disposed diametrically oppositeeach other. The arms 142 have windows 143 for the energy storingelements 137 of the damper 135. Each arm 142 is disposed between a pairof sections 140 (see FIG. 3). To this end, the sections 140 of each pairare provided with confronting pockets 145 jointly defining a receptacleor socket for the respective arm 142. The dimensions of the pockets 145are selected in such a way that the input and output members 138, 139 ofthe damper 135 have limited freedom of angular movement relative to eachother. This is shown in FIG. 5 wherein the two end positions of each ofthe arms 142 relative to the respective pair of sections 140 areindicated by phantom lines, as at 146.

The piston 136 is provided with an annulus of circumferentially spacedapart axial projections 147 (FIG. 3) which extend toward the turbine 118and abut circumferentially spaced apart portions 144 (FIG. 4) of theimmediately adjacent sections 140 of the input member 138. The rivets141 secure the portions 144 of the sections 140 forming part of theinput member 138 to the adjacent axial projections 147 of the piston136.

The median portions of the sections 140 forming part of the input member138 are provided with windows 148 for the adjacent energy storingelements 137. The windows 148 are in accurate axial alignment with thewindows 143 in the arms 142 of the output member 139 and the dimensionsof the windows are selected in such a way that the energy storingelements 137 are received therein without play, i.e., each energystoring element 137 begins to store energy (or to store additionalenergy) as soon as the input and output members 138, 139 begin to turnrelative to each other, i.e., as soon as the arms 142 of the outputmember 139 begin to leave their central positions in the respectivepairs of pockets 145. However, it is equally within the scope of theinvention to select the dimensions of the energy storing elements 137and/or the dimensions and relative positions of the windows 143 and 148in such a way that at least one of the elements 137 is received in therespective windows 143, 148 with at least some clearance. Furthermore,at least one of the energy storing elements 137 can be installed in therespective windows 143 and 148 in at least slightly prestressedcondition. Such expedients render it possible to select the manner inwhich the energy storing elements 137 undergo compression and/oradditional compression while the input and output members 138, 139 ofthe damper 135 turn relative to each other.

An important advantage of the improved dampers 20b and 135 is that theyneed not be designed to transmit the nominal torque of the engine. Thissimplifies the construction and contributes to lower cost for suchdampers.

By way of example, the damper 135 of FIGS. 3 to 5 can be designed insuch a way that its energy storing elements 137 can transmit betweenapproximately 40% and 50% of the nominal (maximum) torque M_(PM) of theengine which drives the cover 116 of the torque converter 111. As can beseen in FIG. 6, the angular movability of the input and output members138, 139 of the damper 135 relative to each other can be selected insuch a way that it need not exceed approximately 5°. FIG. 6 shows theextent of angular movability of the input and output members 138, 139relative to each other while the engine of the motor vehicle is in theprocess of pulling a load (as contrasted with coasting). The extent ofrelative movement of the input and output members 138, 139 duringcoasting of the engine can, but need not, be the same as while theengine is in the process of pulling a load. Furthermore, it is alsowithin the scope of the invention to select the characteristics of theenergy storing elements 137 in such a way that the resistance of theseelements to relative movement of the input and output members 138, 139during coasting is different from the resistance when the engine iscalled upon to pull a load. This can be readily accomplished byappropriate dimensioning of the windows 143 and/or 148 and/or byappropriate selection of the characteristics of the energy storingelements 137. Still further, the torsional damper 135 can be designed insuch a way that it is provided with a multi-stage characteristic curve;for example, one stage of such characteristic curve is or can beeffective while the engine is in the process of pulling a load andanother stage of such characteristic curve is or can be effective whilethe vehicle, wherein the power train between the engine and one or morewheels includes the structure of FIGS. 3 to 5, is coasting.

FIG. 6 further shows that the damper 135 becomes ineffective when theangular displacement of the input and output members 138, 139 of thedamper exceeds approximately 5° as well as that the magnitude of torquewhich can be transmitted while the energy storing elements 137 of thedamper store additional energy does not exceed approximately 45 Nm. Sucha damper 135 can be utilized with advantage in conjunction withhydrokinetic torque converters which employ or cooperate with aslippage-regulated lockup clutch. The torque capacity of approximately45 Nm is particularly suitable when the damper is installed in the powertrain of a vehicle driven by an engine having a nominal torque in therange of between 80 Nm and 200 Nm.

The torque capacity of the damper 135 is preferably selected in such away that it covers the entire main driving range of the motor vehiclehaving a power train between the engine and the transmission, andemploying a damper of the above-outlined character. The term maindriving range is intended to embrace that range of operation of a motorvehicle which is most frequently resorted to during the useful life ofthe vehicle or its engine. Such main driving range preferably embracesat least those ranges of the characteristic performance of the enginewhich are relevant for the FTP75 cycle and/or for the ECE cycle (90 km/hand 120 km/h in city traffic). Thus, the main driving range can becharacterized as that range which is most likely to be in effect whenthe vehicle is in use. The range can vary from country to country inorder to account for specific regulations and traffic infrastructures inthe respective countries.

The diagram of FIG. 7 illustrates the characteristic output curves of atorque transmitting apparatus corresponding to that of FIGS. 3 to 5,i.e., an apparatus employing a so-called "soft" hydrokinetic torqueconverter. The aforediscussed main driving range is denoted by crosshatching with closely adjacent lines. FIG. 7 further shows the torqueconverting range of the torque converter 111. The lockup clutch 112 isnot engaged within the torque converting range of the torque converter111. The hatching denoting the main driving or operating range issurrounded by a hatching denoting that range of operation of the motorvehicle when the lockup clutch 112 is preferably operated with at leastsome (e.g., minimal) slip. The main driving or operating range extendsfrom a lower RPM A to an upper RPM B. The lower RPM A can correspond, atleast substantially, to the idling RPM of the engine (e.g., an RPM inthe range of between about 700 RPM and 800 RPM). The upper RPM B can bewithin the range of between about 2000 RPM and 3000 RPM, e.g., close toor matching 2200 RPM. The slippage of the lockup clutch 112 can beselected in such a way that it ceases at an RPM C, e.g., an RPM whichcan match or approximate the maximum RPM of the engine. However, it ispresently preferred to select the upper limit C in such a way that it isless-than the maximum RPM of the engine; for example, the upper limit Ccan be between about 3000 RPM and 4000 RPM.

FIG. 7 shows that the improved torsion damper 135 can be designed andmounted in such a way that the transmission of torque takes place onlyby way of the lockup clutch 112, i.e., it is not necessary to transmittorque to the hub 114 by way of the cover 116, pump 117 and turbine 118because the lockup clutch 112 operates without slip within the entiremain driving or operating range of the motor vehicle. The energy storingelements 137 of the damper 135 prevent the transmission of anyoscillations of torque from the output element 113 of the engine to theinput shaft of the transmission while the motor vehicle is operatedwithin the main driving range. At the very least, the energy storingelements 137 prevent the transmission of any appreciable oscillations oftorque from the engine to the transmission. The lockup clutch 112 servesmerely to operate with slip in order to compensate for peaks ofoscillations of the torque that is being transmitted by the outputelement of the engine. To this end, the operation of the lockup clutch112 within the main driving range of the motor vehicle is regulated insuch a way that the minimum torque which can be transmitted via thelockup clutch is a relatively small fraction of the nominal torque ofthe engine, but that the maximum torque which the lockup clutch cantransmit is larger than the torque actually being transmitted by theengine to the cover 116 of the hydrokinetic torque converter 111.

That range of operation of the lockup clutch 112 within which thefriction surfaces 121 and 122 are caused to slip relative to each otheris regulated in such a way that the piston 136 and the cover 116 canturn relative to each other, i.e.,that a certain angular displacementtakes place between the turbine 118 and the pump 117. FIG. 7 shows that,when the lockup clutch 112 is operated with slip, it can prevent thetransmission of any undesirable fluctuations of torque from the cover116 to the hub 114 of the turbine 118.

When the operation of the motor vehicle is within the main driving rangeas well as when the lockup clutch 112 is operated with slip, undesirablepronounced fluctuations of torque cannot be transmitted to the inputelement of the transmission by the expedient of reducing the magnitudeof torque which can be transmitted by the lockup clutch. Such pronouncedfluctuations of torque are likely to develop, for example, due toresonance, to an abrupt change of the load and/or for certain otherreasons.

Referring again to FIG. 6, the damper 135 between the lockup clutch 112and the hub 114 of the turbine 118 can be designed in such a way thatthe relatively large angle (of about 5°) within which the frictionsurfaces 121 and 122 offer a relatively low resistance to angularmovements of the piston 136 and cover 116 relative to each other isfollowed by a relatively small angle (e.g., about 2°) of much morepronounced resistance to angular movement of the components 135 and 116relative to one another. For example, the pronounced resistance can beseveral times the relatively low resistance. The relatively small anglecan be greater or less than about 2°. It is presently preferred toselect the pronounced resistance in such a way that it is between aboutseven and fifteen times the relatively low resistance. As can be seen inFIG. 6, the relatively low resistance is or can be about 8 Nm/° and themore pronounced resistance is or can be in the range of about 70 Nm/°.

The magnitude of torque which can be transmitted by the lockup clutch112 within the main driving range (FIG. 7) of the motor vehicle can beselected in such a way that it is between 1.1 and 1.2 times the actualengine torque. The torque which can be transmitted by the clutch 112within the main driving range of the motor vehicle, can be regulated insuch a way that it is not or need not be reduced below a preselectedlower threshold value. Such a value should not be less than 1% of thenominal torque of the combustion engine. For example, the aforementionedlower threshold value can be in the range of about 5 Nm. However, anddepending upon the circumstances of operation of the motor vehicle, thelower threshold value can be higher or lower than 5 Nm. Thus, theminimum torque which the lockup clutch 112 can transmit within the maindriving range of the motor vehicle can be selected in such a way that itis close to, and preferably somewhat less than, the maximum enginetorque which is being transmitted by the output element within the maindriving range of the vehicle.

When the lockup clutch 112 is operated with slip (refer again to FIG.7), the torque which can be transmitted by the clutch can be selected toamount to between about 0.8 times and 0.95 times the momentary enginetorque. Thus, the ability of the lockup clutch 112 to transmit torque isor can be dependent upon the momentary engine torque, i.e., upon thattorque which is to be transmitted by the apparatus 110. Otherwisestated, the torque which the lockup clutch 11 2 should transmitincreases in response to increasing magnitude of the torque beingtransmitted by the output element of the engine. Inversely, themagnitude of torque being transmitted by the lockup clutch 112 decreasesin response to decreasing engine torque.

FIGS. 8 and 9 illustrate a modified lockup clutch 212 which is installedin a hydrokinetic torque converter having a cover or housing 216 and aturbine 218 with a hub 214. The lockup clutch 212 comprises amultiple-stage torsional damper 235 having a first set of energy storingelements 237 and a second set of energy storing elements 250. Theillustrated energy storing elements 237 and 250 are coil springs.

The illustrated lockup clutch 212 is a multidisc clutch having aradially inner disc carrier 251 and a radially outer disc carrier 252.The latter is non-rotatably affixed to the cover 216 of the hydrokinetictorque converter. That portion of the disc carrier 252 which is nearerto the turbine 218 of the torque converter supports a plate-like stop.The cover 216 of the torque converter and the piston 236 of the lockupclutch 212 define a compartment 254 which constitutes a plenum chamberand can receive a body of hydraulic fluid. The pressure in thecompartment 254 determines the magnitude of the torque which is to betransmitted by the lockup clutch 212.

The disc carrier 251 of the multiple-stage damper 235 constitutes theoutput member of the lockup clutch 212 and its radially inner portion isprovided with an annulus of axially parallel teeth 255 mating withclearance with the external teeth 256 provided on the hub 214 of theturbine 218, i.e., on the output element of the hydrokinetic torqueconverter. The external teeth 256 are (or can be) provided on a spurgear which is made of sheet metal and is riveted (as at 262) orotherwise non-rotatably affixed to the hub 214. The multistage damper235 further comprises an input member 238 which is connected with theaforementioned disc carrier or output member 251 of the lockup clutch212. The input member 238 of the multistage damper 235 is an annularcomponent which is provided with radially inwardly extending tongues orprongs 257 received in slit-shaped recesses 258 provided in the outputmember 251 of the lockup clutch 212. The tongues or lugs 257 arereceived in the respective recesses 258 in such a way that theyestablish a practically clearance-free connection between the outputmember 251 of the lockup clutch 212 and the input member 238 of thedamper 235, i.e., the parts 238 and 251 are coupled to each other forrotation about the axis X--X of the lockup clutch 212 and thehydrokinetic torque converter including the cover 216 and the turbine218. FIG. 8 shows that the input member 238 of the damper 235 isprovided with windows 259, 260' for the energy storing elements 237 and250, respectively. The dimensions of the windows 260' and of the energystoring elements 250 are selected in such a way that the elements 250are received in the respective windows 260' with clearance in clockwiseand counterclockwise directions. The annular input member 238 isdisposed between two discs or lamellae 260 and 261 of the lockup clutch212. The discs 260, 261 have confronting cupped portions at the radiallyouter portion of the input member 238 and are riveted to one anotherradially outwardly of the member 238 (see FIG. 9).

The disc 261 is adjacent the turbine 218 and extends radially inwardlyall the way to the hub 214 and is non-rotatably affixed to such hub bythe aforementioned rivets 262. FIG. 9 shows that the rivets 262 serve asa means for non-rotatably affixing the disc 261, the gear 256 and theshell 218a of the turbine 218 to the hub 214.

The characteristic curve of the torsional damper 235 can correspond tothat indicated by the lines or curves 263 and 264 in the diagram of FIG.6.

The curve 263 denotes that range of operation of the damper 235 whichinvolves the storage of energy (or additional energy) by the energystoring elements 237. When the extent of relative angular displacementof the input member 238 and the output member 251 of the damper 235exceeds 5°, the range of operation of the energy storing elements 250begins (curve 264 in FIG. 6), i.e., the elements 250 begin to storeenergy (or additional energy) simultaneously with further stressing ofthe energy storing elements 237. The resistance of energy storingelements 250 to deformation (or to additional deformation) can exceed,even considerably, the resistance of the energy storing elements 237.This is indicated by the slope of the curve 264 in the diagram of FIG.6, i.e., the slope of the curve 264 is much more pronounced than that ofthe curve 263. When the total extent of relative angular displacement ofthe input and output members 238 and 251 exceeds 7° (reference being hadagain to FIG. 6), the internal teeth 255 of the output member 251 engagethe adjacent external teeth of the gear 256 on the hub 214 to thusestablish a form-locking connection between the output member 251 andthe hub 214. All this takes place while the input member 238 turnsrelative to the output member in one direction. Thus, the damper 235 isat least substantially bypassed when the teeth 255 of the output member251 begin to transmit torque directly to the teeth of the gear 256because the transmission of torque no longer takes place by way of theenergy storing elements 237 and 250. Such design of the damper 235 isdesirable and advantageous because the stressing of the energy storingelements 237, 250 cannot exceed a preselected value. The same appliesfor the application of stresses to the input member 238 and discs orlamellae 260, 261.

The aforedescribed novel design and mode of operation of the lockupclutch 12, 112 or 212 and of the damper 20b, 135 or 235 exhibit theimportant advantage that they render it possible to considerably reducethe energy requirements of a motor vehicle embodying a power train whichincludes the improved torque transmitting apparatus. Considerablereductions of the energy requirements of such motor vehicle areattributable to the fact that, when the motor vehicle is operated withinthe main driving range, the lockup clutch is operated without slippage.This is in direct contrast to heretofore known proposals according towhich the lockup clutch is to be operated with slippage within the maindriving or operating range of the motor vehicle. In many instances, themain driving range is, between approximately 600 RPM (lower limit) and2200-3000 RPM (upper limit). The average RPM within such a main drivingrange is or can be approximately 1800 revolutions per minute. Inaccordance with the instant invention, the lockup clutch 12, 112 or 212operates without slippage within the entire (or at least within themajor part of the) main driving range of the motor vehicle. Accordingly,the entire torque which is being transmitted by the output element ofthe prime mover is transmitted to the input element of the transmissionwithout any, or with minimal, slippage of the lockup clutch. Damping ofoscillations (if any) of transmitted torque is effected by the damper20b, 135 or 235. As already described hereinbefore, the angle ofrelative rotation of the input and output members of the damper isrelatively small; when such angle is reached, the damper acts not unlikea rigid body and this preferably takes place at the upper limit of themain driving range of the motor vehicle. Depending on thecharacteristics (such as the horsepower) of the combustion engine orother engine and the weight of the motor vehicle, the upper limit of themain driving range can amount to between about 15% and 50% of thenominal torque of the engine.

A damper which is constructed, assembled, installed and operated in theaforedescribed manner exhibits the additional advantage that iteliminates or at least greatly reduces the likelihood of the developmentof humming, buzzing and like undesirable noises. This is due to the factthat the damper can compensate for oscillations of the torque which isbeing transmitted by the output element of the engine when the magnitudeof such torque is relatively low. Furthermore, the feature that themaximum angle of displacement of the input and output members of thedamper relative to each other is rather small ensures that anyundesirable reaction of the power train to changes in load is minimal oris fully compensated for by the damper and/or clutch. Shocks which areattributable to changes in load are limited or fully compensated forbecause, when the upper limit of the ability of the damper to absorboscillations of transmitted torque is reached or exceeded, the frictionsurfaces of the lockup clutch begin to slip relative to each other tothus limit the magnitude of the torque which can be transmitted by thecombination of lockup clutch and torsional damper. Peaks of transmittedtorque are absorbed by the lockup clutch in that the friction surfacesof the clutch simply turn relative to each other.

If the magnitude of torque which is being transmitted by the outputelement of the engine or another prime mover exceeds the upper limit ofthe torque which is being transmitted within the main driving range ofthe motor vehicle, the friction surfaces of the lockup clutch sliderelative to one another; this ensures that the slippage of the lockupclutch compensates for undesirable reactions which are attributable topronounced changes of load.

When the RPM of the engine is within a range above the main drivingrange of the motor vehicle, the lockup clutch preferably becomes engagedin response to the transmission of a torque which is greater than themomentary torque transmitted by the output element of the engine,provided that the transmitted torque is not caused to oscillate beyond aselected range. If undesirable oscillations develop within certain RPMranges of the output element of the engine, the lockup clutch ispreferably designed to operate with slip. Such a mode of operation ofthe lockup clutch can be resorted to with particular advantage when theRPM matches or approximates the resonance RPM.

It is also possible, and often desirable, to disengage the lockupclutch, or to considerably reduce the magnitude of torque which can betransmitted by the lockup clutch, within the main driving range of themotor vehicle, i.e., when the torque being transmitted by the outputelement of the engine is relatively small, for example, when the RPM ofthe engine matches or approximates the resonance RPM.

The aforedescribed construction and mode of operation of the improvedlockup clutch and of the combination of such lockup clutch with theaforedescribed damper render it possible to eliminate (or at leastminimize) the humming and other noises which develop when a conventionallockup clutch is operated with slip, namely when the friction surfacesof a conventional clutch are caused to move relative to each other insuch a way that intervals of slippage alternate with intervals ofadherence of neighboring friction surfaces to each other.

The features which are shown in the drawings can be combined with and/orsubstituted for each other without departing from the spirit of theinvention. The same applies for the various methods of assembling theimproved torque transmitting apparatus, of operating the apparatus, ofdesigning and operating the lockup clutch and of designing and operatingthe torsional damper. The same holds true for a combination ofheretofore described apparatus with those described and shown in thecommonly owned German patent application No. 43 28 182.6.

The manner in which the output element of an engine can be attached tothe cover of the torque converter and/or the manner of establishing atorque transmitting connection between the turbine and the input elementof a transmission forms no part of the present invention. The sameapplies for the details of various valves which can be utilized toregulate the flow of fluid into and from the housing of the torqueconverter.

The improved damper 20b, 135 or 235 exhibits a number of importantadvantages. Thus, the damper can absorb or compensate for at least ahigh percentage of those oscillations and/or other undesirablevariations or fluctuations of torque which are transmitted by the lockupclutch 12, 112 or 212. At any rate, the damper can absorb or filter theundesirable variations or fluctuations or oscillations of torque beingtransmitted by the lockup clutch so that the fluctuations (if any) oftorque which are being transmitted by the damper are within anacceptable range. The torque capacity of the damper, i.e., the maximumtorque transmittable by the energy absorbing elements (such as the coilsprings 237 and 250) of the damper, is less than the nominal (i.e.,maximum) torque transmittable by the prime mover and its output element(such as the rotary output element 13 shown in FIG. 1). Otherwisestated, and in contrast to prior proposals, the damper which is utilizedin the apparatus of the present invention and enables such apparatus tobe used for the practice of the methods of the present invention neednot be designed to transmit torque when the prime mover is operated at amaximum load. When the torque capacity of the damper is reached orexceeded, the lockup clutch or at least the damper which cooperates withor forms part of such lockup clutch acts not unlike a rigid body, i.e.,the damper transmits the entire torque which is being transmitted to itsinput member. Due to the fact that the damper is not called upon totransmit the entire torque but is effective only within one or moreportions of the entire range of torques being transmitted to the inputelement of the variable-speed transmission or another driven unit, theeconomy, the compactness, the reduction of weight, the lengthening ofuseful life, the simplicity and certain other desirable parameters ofthe damper can be enhanced to a surprising extent. For example, it ispossible to employ a damper which is equipped with relatively weak coilsprings and/or other suitable energy storing elements. This, in turn,renders it possible to reduce the space requirements, the weight and thecost of such energy storing elements as well as the cost, weight andspace requirements of the entire torque transmitting apparatus. Asalready mentioned above, it is possible to limit the magnitude of torquewhich can be transmitted by the damper 20b, 135 or 235 by permitting theconvolutions of its coil springs to come into full abutment with eachother. However, and as also mentioned above and as shown, for example,in FIGS. 8 and 9, the damper and/or one or more other constituents ofthe improved apparatus can be provided with means (such as the teeth255, 256 shown in FIGS. 8 and 9) which prevent any further stressing ofthe resilient energy storing elements when the magnitude of thetransmitted torque reaches or exceeds a preselected torque capacity ofthe damper. A presently preferred damper is designed in such a way thatits torque capacity is between 10% and 60% (e.g., between 25% and 50%)of the nominal torque of the prime mover (e.g., a combustion engine in amotor vehicle). However, it is also possible to employ a damper whosetorque capacity is below 10% or above 60% of the nominal torque of theprime mover.

Another important advantage of the improved damper is that it does notor need not employ any discrete friction generating means. Thus, each ofthe aforedescribed dampers 20b, 135, 235 can be constructed andassembled in such a way that it merely employs an input member, anoutput member and one or more energy storing elements disposed betweenthe input and output members and serving to oppose angular movements ofsuch members relative to one another. Thus, the damper need not employfriction discs or other parts which must rub against each other whilethe input and output members of the damper turn relative to each other.This contributes to a longer useful life of the damper and to areduction of its space requirements. Moreover, the torque capacity ofsuch a damper remains or can remain constant during the entire usefullife of the torque transmitting apparatus.

The aforementioned range of torque capacities of the damper (betweenabout 10% and 60%, preferably between about 25% and 50% of the nominaltorque of the prime mover) have been found to be highly satisfactorywhen the apparatus embodying a hydrokinetic torque converter with alockup clutch and the aforedescribed damper is utilized in the powertrain between the engine and the variable-speed transmission of a motorvehicle. The reason is that the damper is capable of absorbing orcompensating for all or nearly all fluctuations of torque which developor are expected to develop when the actual torque being transmitted bythe engine is not appreciably less than 10% and not appreciably morethan 60% of the nominal torque.

It was further ascertained that the extent of angular displacement ofthe input and output members of a damper which can be utilized withadvantage in the improved torque transmitting apparatus can be much lessthan that of input and output members which form part of dampers inheretofore known torque transmitting apparatus utilizing a hydrokinetictorque converter with a lockup clutch and a damper in the cover of thetorque converter. As explained hereinbefore, the extent of angularmovement between the input and output members (e.g., the input andoutput members 138, 139 of the damper 135 shown in FIGS. 3 to 5) can bewithin the relatively narrow range of between ±2° and ±8°, preferablybetween ±3° and ±6°. Thus, the total angular displacement of the inputand output members relative to each other (in the clockwise andcounterclockwise directions) can be between about 4° and 16° preferablybetween 6° and 12°. Such relatively small angular displacement isparticularly desirable and advantageous when the operation of a motorvehicle embodying the improved torque transmitting apparatus is shiftedfrom coasting to pulling a load or vice versa. Relatively small angulardisplacements of the input and output members of the damper relative toeach other under such circumstances (shifting from pull to coasting orvice versa) reduce the likelihood of, or prevent the development of, anexcessive buildup of resonant vibrations in the power train of the motorvehicle. Any fluctuations of torque beyond the torque capacity of thedamper are compensated for in that the friction surfaces of the lockupclutch are caused to slide relative to each other. Thus, the novelcombination of the lockup clutch and damper is effective within a widerange of operations of a motor vehicle with the improved apparatusbetween the engine and the variable-speed transmission, i.e., the inputelement of the transmission is not likely to be subjected to any, or anypronounced or excessive, fluctuations of torque being transmitted by thehub of the turbine forming part of the hydrokinetic torque converter.

In most instances, the rigidity of the damper can be selected in such away that it is between about 7 Nm/° and 30 Nm/°, preferably betweenabout 8 Nm/° and 15 Nm/°. However, it is also possible (under certainoperating conditions) to utilize a damper with a rigidity of less than 7Nm/°, or more than 70 Nm/°. It has also been ascertained that, at leastunder most circumstances, the torque capacity of the damper can bebetween about 30 Nm and 90 Nm, preferably between about 40 Nm and 70 Nm.If the nominal torque of the prime mover (such as a combustion engine ina motor vehicle) is relatively small, the torque capacity of the dampercan be less, even considerably less, than about 30 Nm. On the otherhand, the torque capacity of the damper can be above, even well above,90 Nm if the cover of the hydrokinetic torque converter receives torquefrom a powerful engine.

One presently preferred method of transmitting torque by way of ahydrokinetic torque converter which is constructed and assembled inaccordance with the present invention and transmits torque to the rotaryinput element (such as 14a) of a variable-speed transmission having atleast one forward shift stage comprises the step of regulating (such asby the processor 32a, regulating unit 32 and valve 31 of FIG. 1) thetransmission of torque by the lockup clutch (such as the clutch 12) as afunction of variations of energy- and/or power-related parameters atleast in the one forward shift stage of the variable-speed transmission.If the variable-speed transmission includes two or more forward shiftstages, the transmission of torque by the lockup clutch can be regulateddepending upon variations of energy- and/or power related parameterswithin two forward shift stages or within each forward shift stage ofthe variable-speed transmission. However, it is equally possible todesign the regulating means for the operation of the lockup clutch insuch a way that the lockup clutch remains disengaged within the firstand/or second forward shift stage(s) of the variable-speed transmission.

The method and apparatus of the present invention can be utilized withadvantage in connection with or in power trains of the type disclosed incommonly owned German patent application No. P 43 28 182.6 and/or incorresponding applications pending or patented in other countriesincluding the United States of America. The disclosure of such Germanpatent application and/or of the corresponding applications in countriesother than Federal Republic Germany is incorporated herein by reference.The aforementioned German patent application discloses variousembodiments of a lockup clutch which can be utilized in a hydrokinetictorque converter and at least some embodiments of such lockup clutch canbe put to use in the apparatus of the present invention.

In accordance with another method of transmitting torque by a slippinglockup clutch in a hydrokinetic torque converter which receives torquefrom an engine, the transmission of torque (e.g., by the components 31,32, 32a of the apparatus shown in FIG. 1) via a lockup clutch can beregulated in a plurality of stages including the transmission of torqueby the lockup clutch in at least two stages (reference may be had againto FIG. 6) one of which involves the transmission of torque within arange of between about 10% and 60% (preferably between about 15% and50%) of the maximum engine torque and another of which involves thetransmission of torque corresponding to at least 60% of the maximumtorque transmitted by the engine. The selection of the magnitude oftorque which the lockup clutch can transmit during the aforementionedstages (with reference to the magnitude of torque being transmitted bythe output element of the engine) can be made dependent on parametersother than those proposed before. For example, the aforementionedcommonly owned German patent application No. P 43 28 182.6 proposes toattribute different importance to one or more parameters duringdifferent stages of torque transmission by the lockup clutch. Suchparameters include a torque dividing factor (K_(mc)), a correctionfactor (K_(korr)) to compensate for multiplicative errors, a correctiontorque (M_(korrMot)) to compensate for errors in addition to enginetorque), and correction torque (M_(korrW0)) to compensate for errors inaddition to clutch torque. In other words, the magnitude of at least oneof the above-enumerated factors (and hence the influence of the at leastone factor upon the torque being transmitted by the lockup clutch) isdifferent during the aforementioned stages. In contrast to such earlierproposal, the first stage of regulation in accordance with theaforediscussed novel method involves the transmission of torque within arange of between about 10% and 60% of a maximum torque transmitted bythe engine during one stage and the transmission of torque correspondingto at least 60% of the engine torque during another stage. The otherstage can immediately follow the one stage.

The magnitude of the torque which the lockup clutch can transmit duringthe one stage can exceed the magnitude of torque actually transmitted bythe engine. It is also possible to regulate the magnitude of the torquetransmitted by the lockup clutch in such a way that the maximum torquetransmittable by the lockup clutch during the one stage matches or atleast approximates the torque capacity of the damper. This ensures thatrelatively small fluctuations of torque transmitted by the outputelement of the engine are compensated for by the damper and the lockupclutch begins to slip when the peaks of oscillations of torque beingtransmitted by the output element of the engine exceed the torquecapacity of the damper. Such slipping of the clutch ensures that atleast the majority if not all of the oscillations of torque beingtransmitted by the output element of the engine cannot affect the torquewhich is being transmitted to the input element of the variable-speedtransmission.

An advantage of the step of selecting the magnitude of the torquetransmittable by the lockup clutch during the one stage to exceed themagnitude of torque actually being transmitted by the engine (i.e., themagnitude of the torque which the engine can transmit depending on thequantity of fuel being supplied to the engine) is that the operation ofthe lockup clutch can be regulated with a view to ensure that the torquebeing transmitted by the lockup clutch within a first range ofrotational speeds of the output element of the engine varies in exact orsubstantial synchronism with variations of the torque transmitted by theoutput element of the engine. Thus, the magnitude of the torque whichthe lockup clutch can transmit decreases in response to decreasingtorque which is being transmitted by the output element of the engine,but the magnitude of the torque which the lockup clutch can transmitexceeds the torque actually being transmitted by the output element ofthe engine. Analogously, the magnitude of torque which the lockup clutchcan transmit increases in response to increasing magnitude of the torqueactually being transmitted by the output element of the engine. It hasbeen found that the torque which the lockup clutch transmits during theone stage (within a first range of rotational speeds of the engine) canbe between 1 and at least 1.2 times the torque being simultaneouslytransmitted by the engine.

It is also possible to regulate the magnitude of torque beingtransmitted by the lockup clutch in such a way that it remains at leastsubstantially constant within the aforementioned one range or firstrange and that it is within between about 25% and 60% (preferablybetween about 30% and 50%) of the maximum torque of the engine. Theconstant torque which the lockup clutch can transmit within the onerange can at least match but preferably exceeds the torque capacity ofthe damper; for example, the constant torque transmitted by the lockupclutch can be between 1.05 and 1.2 times the torque capacity of thedamper.

In accordance with still another modification, the magnitude of thetorque which the lockup clutch can transmit during a first part of theone stage (preferably while the RPM of the output element of the engineis immediately above the idling RPM of the engine) remains at leastsubstantially constant, whereas the magnitude of torque which the lockupclutch can transmit during a second part of the one stage varies in atleast substantial synchronism with variations of torque being thentransmitted by the output element of the engine. Thus, if the magnitudeof the torque transmitted by the engine during the second part of theone stage increases, the capacity of the lockup clutch to transmit alarger torque also increases. The arrangement is preferably such thatthe magnitude of torque which the lockup clutch can transmit during theaforementioned second part of the one stage at least matches butpreferably somewhat exceeds the momentary torque being transmitted bythe output element of the engine.

In order to ensure a highly accurate regulation or control of torquewhich can be transmitted by the lockup clutch, it can be of particularadvantage to ensure that the minimum torque transmittable by the lockupclutch, at least within a portion of the one range of torquestransmittable by the engine, is not less than approximately 1% of thenominal torque of the engine and is preferably at least slightly above1%. This ensures that the fluid pressure for the lockup clutch does notdrop below a lower threshold value, namely that the fluid pressure isnot less than that which can be satisfactorily selected and regulated byavailable valves, e.g., valves of the character shown in FIG. 1. Thus,by resorting to the novel expedient of ensuring that the minimum torquewhich the lockup clutch can transmit is not less than at least 1% of thenominal torque of the engine, one can regulate the fluid pressure with ahigh degree of accuracy.

As already mentioned hereinbefore, the first range of rotational speedsof the output element of the engine can extend between the idling RPMand not more than 3000 RPM, preferably between idling RPM and 2000-2500RPM. Here, again, it might be desirable (under certain specificcircumstances) to select the first range of rotational speeds in such away that its upper limit is above 3000 RPM or below 2000 RPM.

It is also possible to select the torque which can be transmitted by thelockup clutch in such a way that the damper is effective (eitherprimarily or exclusively) within a first or lower part of the entireoperating range of the torque transmitting apparatus and that the lockupclutch takes care of oscillations of torque being transmitted by theoutput element of the engine within a second or higher part whichimmediately follows the first part. In other words, the lockup clutchwill be operated with slip if the oscillations of transmitted torquewithin the second part of the entire operating range of the torquetransmitting apparatus are sufficiently pronounced to warrant acompensation by causing or permitting the lockup clutch to operate withslip. Furthermore, it is also possible to design the damper in such away that it can be caused to damp oscillations during the aforementionedsecond part of the operating range of the torque transmitting apparatus.All that is necessary is to ensure that the energy storing elements ofthe damper can dissipate stored energy prior to transition or duringtransition from the first part to the second part of the operating rangeof the apparatus so that the energy storing elements can store energyagain within that part of the operating range when the transmission ofexcessive fluctuations of torque from the output element of the engineto the input shaft of a variable-speed transmission or another drivenunit is prevented by causing the lockup clutch to operate with slip. Ifthe damper is designed in the just-outlined manner, it is presentlypreferred to ensure that the lockup clutch takes care of the major partof the task of preventing the transmission of fluctuations of torque tothe driven unit within the second part of the operating range of thetorque transmitting apparatus.

As a rule, the damper will be designed to operate or to be effectiveprimarily within the first part of the operating range of the apparatus,and its torque capacity is normally between 10% and 60% (preferablybetween 15% and 50%) of the nominal torque of the engine. In accordancewith a further feature of the invention, the damper can be constructed,assembled and operated in such a way that its input and output memberscan turn relative to each other through a first angle within theaforementioned first part of the operating range of the apparatus andthereupon through a relatively small second angle at which time thegradient of its energy storing elements (such as coil springs) is muchsteeper, i.e., the characteristic curve of the energy storing elementsduring angular movement of the input and output members relative to eachother within the second angle is much steeper than the characteristiccurve during angular movement through the larger first angle. Such adesign of the torsional damper ensures that the parts (such as the teeth255, 256 shown in FIGS. 8 and 9) are much less likely to impact againsteach other with a considerable force, such as could result in thegeneration of undesirable noise and/or in damage to and shorter usefullife of the damper. The first angle can be between 2 and 5 times largerthan the second angle; a presently preferred ratio is approximately 2.5to 1. The rigidity of the damper while its input and output members turnrelative to each other through the preferably smaller second angle canbe between four and ten times the rigidity of the damper (i.e., of theenergy storing elements of the damper) when the input and output membersturn relative to each other through the preferably larger first angle.In many instances, it suffices if the rigidity during angulardisplacement through the second angle is between about two and fivetimes the maximum rigidity at the end of first angular movement of theinput and output members relative to each other. In any event, it ispresently preferred to select the torque capacity of the damper in sucha way that it is less than the nominal torque of the engine. Themagnitude of the second angle can be between about 0.5° and 3°,preferably between 1° and 2°. It is also possible to design the energystoring elements of the damper in such a way that the damper iseffective only while the vehicle embodying an engine and the improvedtorque transmitting apparatus is in the process of pulling a load.

The aforediscussed drawback of conventional torque transmittingapparatus that the lockup clutch generates readily detectable humming orsimilar noise (because its friction surfaces alternately adhere to andslide relative to each other, particularly when the apparatus is in theprocess of transmitting relatively small torques) is believed to havebeen overcome in that the damper 20b, 135 or 235 is effective to absorbfluctuations of torque being transmitted by the output element of theengine if and when the friction surfaces of the lockup clutch tend toadhere to each other at a time when the fluctuations of torque wouldnormally be absorbed or counteracted by the lockup clutch.

The improved apparatus can be designed in such a way that the lowerlimit of the range of operation of the lockup clutch with slip islowered when a motor vehicle embodying the improved apparatus isoperated under circumstances such that the torque being transmitted bythe output element of the engine at a relatively low RPM (e.g.,immediately above the idling RPM) fluctuates within a wide range, e.g.,at resonance RPM and/or in response to changes of the load upon thevehicle. If necessary, the magnitude of the torque transmittable by thelockup clutch when the engine is coasting can be reduced all the way orat least close to zero in response to changes of load upon the vehicle.It is also possible to reduce (if necessary) the magnitude of the torquebeing transmittable by the lockup clutch within the aforediscussedsecond or higher range of rotational speeds of the engine.

As already mentioned above, the apparatus of the present invention canbe designed in such a way that at least a major part of a first range oftorques is transmitted from the output element of the engine to theinput element of a driven unit within the main driving or operationalrange of the engine, or that at least a major part of the characteristiccurve of the engine is within the first range of torques. It ispreferred and advisable that the main driving range of the engineembrace or encompass at least those regions of the characteristic curvewhich are relevant for the FTP75 cycle and/or for the ECE cycle coveringtransport on city, state and interstate roads (90 km/h in the city and120 km/h outside of city limits). Such design ensures that thetransmission of oscillations of torque is prevented (either entirely orprimarily) by the damper within the entire main driving range, i.e.,that the torque converter is bypassed practically uninterruptedly which,in turn, results in more economical operation of the vehicle because theenergy requirements of the engine are lower. Such a mode of operation isnot contemplated by the makers of heretofore known torque transmittingapparatus which employ a slipping lockup clutch because the lockupclutch of such conventional apparatus is supposed to slip within the RPMrange immediately above the idling RPM. This can be readily ascertainedby referring to the prior publications which are mentioned in thepresent specification under the heading "BACKGROUND OF THE INVENTION".It has been found that the transmission of oscillations of torque to theinput element of a driven unit can be prevented much more effectively ifthe damper is operative within the main driving range of the vehicle,i.e., if the damper is constructed, assembled and operated in such a waythat it is operative, either primarily or exclusively, within the maindriving range of the motor vehicle. Such a damper is much more effectivethan a damper which is designed to counteract oscillations of torquewithin as well as above the main driving range of the vehicle. Moreover,a damper which is designed to be operative, mainly or exclusively,within the main driving range of the vehicle is simpler and more compactthan the dampers which are proposed for use in conventional torquetransmitting apparatus.

The torque which the lockup clutch can transmit within the second orhigher range of rotational speeds of the output element of the enginecan be between 0.6 and 1 times (preferably between 0.8 and 0.9 times)the then prevailing torque of the engine. Thus, the torque which thelockup clutch can transmit during the aforementioned second range shouldbe less than the momentary torque being transmitted by the outputelement of the engine. Such mode of operation of the lockup clutchensures that the latter operates with some slight slippage within thesecond range of rotational speeds of the output element, i.e., that theclutch is then effective to absorb or to compensate for fluctuations (ifany) of the torque being transmitted by the output element of theengine.

If the improved apparatus is installed in a so-called uncritical motorvehicle (namely a vehicle whose engine is not likely to transmitfluctuating torque within the second range of rotational speeds of theoutput element), the lockup clutch can remain engaged or practicallyengaged, i.e., the torque being transmitted by the clutch can correspondto the torque being then transmitted by the output element of theengine. As a rule, the magnitude of the torque which the lockup clutchcan transmit will be slightly larger than the magnitude of the torqueactually being transmitted by the output element, e.g., between 1 and1.2 times the torque being transmitted by the output element.

The preceding paragraphs of this specification refer to two RPM rangesincluding a first range immediately above the idling RPM and a secondrange immediately above the first range. However, it is equally withinthe scope of the invention to divide the entire spectrum of rotationalspeeds of the engine above the idling RPM into more than two (first andsecond) ranges. For example, the second range can consist of twonarrower ranges including a lower range and a higher range. The torqueconverter is then fully bypassed during the higher range and the lowerlimit of such higher range is or can be selected in such a way that thetorque then being transmitted by the engine is not likely to requirecompensation for un desired oscillations such as would necessitateslippage of the lockup clutch.

In accordance with a further feature of the invention, the improvedapparatus for transmission of torque from the rotary output element ofan engine to the rotary input element of a variable-speed transmissionhaving a plurality of speed ratios can comprise a hydrokinetic torqueconverter with an engageable and disengageable lockup clutch and meansfor monitoring the speed of the motor vehicle in which the engine andthe torque converter are installed. The monitoring means can be designedto ascertain whether or not a disengagement of the lockup clutch at aparticular speed would contribute to an increase of the towing force(i.e., traction or traction force or pulling force) of the vehicle byway of the torque converter without a change of the speed ratio of thevariable-speed transmission, and such monitoring means can disengage thelockup clutch when the disengagement of the clutch contributes to theincrease of the towing force. Still further, the monitoring means can bedesigned to shift the variable-speed transmission into a lower speedratio when the disengagement of the lockup clutch does not contribute tothe aforementioned increase of the towing force. Such monitoring meanscan be designed to carry out the above-outlined operations at leastwhile the vehicle is being accelerated. The lockup clutch can bedisengaged, at least in part, when the monitoring means is caused toshift the variable-speed transmission into a lower speed ratio, i.e.,the lockup clutch is then operated with a certain amount of slip. Themonitoring means can include an electronic computer or processor and oneor more sensors which actually monitor one or more variable parameters.At least some of these parameters can be stored in the memory of thecomputer or processor in the form of charts, maps or characteristiccurves. For example, the memory of the computer or processor can storethe characteristic curves of the torque converter and/or the engineand/or the lockup clutch. As shown in FIG. 1, the operating condition ofthe engine can be monitored by ascertaining its rotational speed, theinclination of the pivotable valving element of the throttle valve(i.e., the quantity of fuel being supplied to the engine), the pressurein the suction pipe and/or, if necessary, the timing of fuel injection.All of the details of such an electronic computer or processor aredisclosed in the aforementioned copending German patent application No.P 43 28 182.6 and in the corresponding patent applications filed incountries other than Federal Republic Germany. As mentionedhereinbefore, the disclosures of such pending applications (or patentsgranted on such applications) are incorporated herein by reference.

The torque converter of the improved apparatus can be fully bypassedwhen the RPM of the engine rises to a certain value, i.e., when thespeed of the motor vehicle rises to a predetermined value. The apparatusthen acts as a substantially rigid torque transmitting assembly and thisdoes not affect the comfort and/or other desirable characteristics ofthe vehicle because, as a rule, the fluctuations of torque are not verypronounced when the engine speed (i.e., the speed of the motor vehicle)reaches the aforementioned value. The lockup clutch of such apparatus isdesigned to operate with slip when the speed of the engine reaches theaforementioned value, preferably in such a way that the clutch begins toslip when the torque being transmitted thereto at least approximates orexceeds the engine torque.

As already mentioned before, the torsional damper which is constructed,assembled, installed and operated in accordance with the presentinvention and the lockup clutch which cooperates with such damper ensurethat, when the engine is operated under partial load and fluctuations oftransmitted torque caused by alternating slippage and full engagement ofthe friction surfaces of the clutch relative to each other could entailthe generation of undesirable noise, the damper compensates forintermittent full engagement of the lockup clutch at a time when thefriction surfaces of the clutch should slide relative to each other sothat the generation of noise is reduced to or at least approximateszero. Furthermore, the apparatus is unlikely to transmit abrupt or jerkyvibrations when the engine is operated under partial load. As a rule,the "softness" of the damper will be selected depending upon theparameters of the engine in which the apparatus is to be put to use. Ifthe torsional damper encompasses a resonance range which is covered whenthe vehicle is in operation, the lockup clutch is preferably designed tooperate with slip within such resonance range. This also contributes toa reduction or full elimination of humming and/or other noises when thetorque transmitting apparatus is in use.

The changes of load within the first range of rotational speeds of theoutput element of the engine above the idling RPM are limited due to therelatively small angle of displacement of the input and output membersof the damper relative to each other and also because the lockup clutchbegins to slide in response to the application of a torque which isrelatively low when compared with the maximal torque of the engine.Thus, the ability of the lockup clutch to transmit torque within the RPMrange immediately above the idling RPM can be selected in such a waythat it is only slightly above the torque being then transmitted by theengine. Hence, the lockup clutch can counteract the tendency of thepower train embodying the novel apparatus to oscillate in response tochanges of load. When the RPM of the output element of the engine risesto a higher value (i.e., when it is within the aforediscussed secondrange) because the load upon the engine is higher, the maximum torquewhich the lockup clutch can transmit is less than the then prevailingengine torque, i.e., the lockup clutch then operates with slip. Suchslippage also reduces the likelihood of the development of noise, atleast within a certain range of torques, because the friction surfacesof the lockup clutch slide relative to each other without recurringintervals of non-slippage.

The construction of the improved apparatus is preferably such that thetorque converter is bypassed within the entire operating range of theengine (such as a combustion engine) only when this is advisable inorder to save energy. The reason is that it is advisable, during certainstages of operation of the engine, to avoid any (even partial) bypassingof the torque converter. Furthermore, the lockup clutch is engaged whenthe driver of a vehicle embodying the improved torque transmittingapparatus is in the process of accelerating the engine in order toeffect a change of the transmitted torque.

The improved apparatus preferably employs a so-called "soft" torqueconverter. The characteristic features of a "soft" torque converter aredescribed in the aforementioned commonly owned German patent applicationNo. P 43 28 182.6. The utilization of a "soft" torque converter rendersit possible to achieve a more satisfactory acceleration of a motorvehicle because the torque converter has a wider torque conversionrange. Moreover, the efficiency is more satisfactory within a largerpart of the operating range of a "soft" torque converter than theefficiency of a conventional apparatus employing a "hard" torqueconverter. The "soft"=0 torque converter renders it possible to reducelosses of output and to thus reduce the consumption as well as thetemperature of the fluid (normally oil) which is being admitted into thecover or housing of the torque converter (e.g., by way of the conduit 30shown in FIG. 1). The lower-efficiency range of a "soft" torqueconverter is bypassed by the simple expedient of engaging the lockupclutch to an extent which allows certain slippage of the frictionsurfaces relative to each other while the clutch receives torque fromthe output element of the engine. It has been found that theabove-outlined "soft" torque converter and a lockup clutch which slipswithin the lower-efficiency range of the torque converter ensure thatthe efficiency is more satisfactory and the losses of output are lowerduring each stage of operation of a vehicle embodying such torquetransmitting apparatus. Since the lockup clutch can be caused to beeffective in each speed ratio of the variable-speed transmission, theenergy requirements of a motor vehicle with a power train which embodiesthe improved apparatus are not higher than those of a motor vehicle witha power train which does not employ a hydrokinetic torque converter.

The block diagram of FIG. 10, like FIG. 1, shows a computer apparatus32a which determines, at least during acceleration of a motor drivenvehicle, if opening of the lockup clutch 12 will increase the torquedelivered by the torque converter while the transmission is in the samegear. In order to accomplish this, the system input variables aremeasured and monitored. Also, information on the torque converter, e.g.in the form of a performance graph of the torque converter 10 under bothopened and closed conditions, is forwarded to the computer 32a whichcalculates whether the opening of the lockup clutch guarantees anincrease of torque in the same gear. If this is not the case at therespective point of operation, then at least the transmission is setback by one gear.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of the prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of theabove-outlined contribution to the art and, therefore, such adaptationsshould and are intended to be comprehended within the meaning and rangeof equivalence of the appended claims.

What is claimed is:
 1. Apparatus for transmitting torque from a rotaryoutput element of a prime mover, comprising a hydrokinetic torqueconverter including a lockup clutch having a torsion damper with atorque capacity less than a nominal torque of the prime mover.
 2. Theapparatus of claim 1, wherein said torque capacity is between 10% and60% of the nominal torque of the prime mover.
 3. The apparatus of claim2, wherein said torque capacity is between 25% and 50% of the nominaltorque of the prime mover.
 4. The apparatus of claim 1, wherein saiddamper is devoid of discrete friction generating means.
 5. The apparatusof claim 1, wherein said damper includes rotary input and output membersrotatable relative to each other through an angle of between about ±2°and ±8°.
 6. The apparatus of claim 1, wherein said damper includesrotary input and output members rotatable relative to each other throughan angle of between about ±3° and ±6°.
 7. The apparatus of claim 1,wherein said damper has a rigidity of between about 7 Nm/° and 30 Nm/°.8. A method of transmitting torque by a lockup clutch in a hydrokinetictorque converter which receives torque from an engine, comprising thestep of regulating the transmission of torque by the lockup clutch intwo stages one of which involves the transmission of torque within arange of between about 10% and 60% of a maximum torque transmitted bythe engine and the other of which involves the transmission of torquecorresponding to at least 60% of the maximum torque transmitted by theengine.
 9. The method of claim 8, wherein said one stage involves thetransmission of torque by the lockup clutch within a range of betweenabout 15% and 50% of the maximum torque transmitted by the engine. 10.The method of claim 8, wherein the magnitude of the torque which thelockup clutch can transmit during said one stage exceeds the magnitudeof torque actually being transmitted by the engine.
 11. The method ofclaim 10, wherein the magnitude of torque which the lockup clutchtransmits during said one stage is between 1 and at least 1.2 times themagnitude of torque being simultaneously transmitted by the engine. 12.Apparatus for transmitting torque from a rotary output element of anengine, comprising a hydrokinetic torque converter including a lockupclutch and a torsional damper arranged to take up fluctuations of torquewithin a first range of torques transmitted by the output element, saidlockup clutch being operative to slip in response to fluctuations oftorque within a second range of torques being transmitted by said outputelement.
 13. The apparatus of claim 12, further comprising means forreducing the magnitude of torque adapted to be transmitted by saiddamper within said first range of torques in response to pronouncedoscillations of torque transmitted by a power train including saidtorque converter.
 14. The apparatus of claim 13, wherein said means forreducing the magnitude of torque is responsive to resonance RPM andchanges of load upon the engine.
 15. Apparatus for transmitting torquefrom a rotary output element of an engine, comprising a hydrokinetictorque converter including a turbine, a lockup clutch having an inputmember receiving torque from said output element, and a torsional damperbetween an output member of said clutch and said turbine, said damperbeing arranged to take up fluctuations of torque within a first range ofa plurality of ranges of torques being transmittable by the outputelement and having a torque capacity at least approximating an upperlimit of said first range, said lockup clutch being operative to slip inresponse to fluctuations of torque within a second range of saidplurality of ranges.
 16. The apparatus of claim 15, wherein the minimumtorque transmittable by said clutch within a portion at least of saidfirst range of torques transmittable by the engine at least equals 1% ofthe nominal torque of the engine.
 17. The apparatus of claim 15, whereinthe torque transmitted by said clutch within a portion at least of saidfirst range of torques transmittable by the engine is at leastsubstantially constant.
 18. The apparatus of claim 15, wherein theengine has a main driving range and at least a major part of said firstrange of torques is transmitted within said main driving range.
 19. Theapparatus of claim 15, wherein said first range of torques is beingtransmitted while the engine is driven within an engine RPM rangebetween idling RPM and about 3000 RPM.
 20. The apparatus of claim 19,wherein said first range of torques is being transmitted within anengine RPM range between idling RPM and 2000-2500 RPM.
 21. The apparatusof claim 15, wherein said plurality of ranges further embraces a secondrange of torques transmittable by the engine and the torque transmittingcapacity of said clutch within said second range is between about 0.6and 0.99 times the actual torque being transmitted by the output elementof the engine.
 22. The apparatus of claim 21, wherein the torquetransmitting capacity of said clutch within said second range is between0.8 and 0.9 times the actual torque being transmitted by the outputelement of the engine.
 23. Apparatus for transmitting torque from arotary output element of an engine in a motor vehicle to a rotary inputelement of a variable-speed transmission having a plurality of speedratios, comprising:a hydrokinetic torque converter including anengageable and disengageable lockup clutch; means for monitoring thespeed of the vehicle; means for ascertaining whether a disengagement ofthe lockup clutch at a particular speed contributes to an increase ofthe traction force of the vehicle by way of said torque converterwithout a change of the speed ratio of the variable-speed transmission;means for disengaging the clutch when the disengagement of the clutchcontributes to said increase of the traction force; and means forshifting the variable-speed transmission into a lower speed ratio whenthe disengagement of the clutch does not contribute to said increase ofthe traction force.
 24. The apparatus of claim 1, wherein said primemover includes an engine and further comprising means for regulating thetransmission of torque by said lockup clutch in two stages one of whichinvolves the transmission of torque within a range of between about 10%and 60% of a maximum torque transmitted by said engine and the other ofwhich involves the transmission of torque corresponding to at least 60%of the maximum torque transmitted by said engine.
 25. The apparatus ofclaim 24, wherein said one stage involves the transmission of torque bysaid lockup clutch within a range of between about 15% and 50% ofmaximum torque transmitted by said engine.
 26. The apparatus of claim 1,wherein said prime mover includes an engine and said torsion damper ispart of said lockup clutch, said torsion damper having means for takingup fluctuations of torque within a first range of torques beingtransmitted by said output element, said lockup clutch being operativeto slip in response to fluctuations of torque within a second range oftorques being transmitted by said output element.
 27. The apparatus ofclaim 26, further comprising means for reducing the magnitude of torqueadapted to be transmitted by said damper within said first range oftorques in response to pronounced oscillations of torque beingtransmitted by a power train including said torque converter.
 28. Theapparatus of claim 1, wherein said prime mover includes an engine, saidtorque converter further including a turbine and said lockup clutchfurther having an input member receiving torque from said outputelement, said torsion damper being disposed between an output member ofsaid clutch and said turbine and said torque capacity at leastapproximating an upper limit of a first range of a plurality of rangesof torque being transmitted by said engine.
 29. Apparatus fortransmitting torque from a rotary output element of a prime moverincluding an engine, comprising a hydrokinetic torque converterincluding a lockup clutch having a torsion damper with a torque capacityless than a nominal torque of said engine, said torque converter furtherincluding a turbine and said lockup clutch further having an inputmember receiving torque from said output element, said torsion damperbeing disposed between an output member of said clutch and said turbineand said torque capacity at least approximating an upper limit of afirst range of a plurality of ranges of torque being transmitted by saidengine, the torque being transmitted by said clutch within a portion atleast of said first range of torques transmittable by said engine beingat least substantially constant.
 30. Apparatus for transmitting torquefrom a rotary output element of a prime mover including an engine,comprising a hydrokinetic torque converter including a lockup clutchhaving a torsion damper with a torque capacity less than a nominaltorque of said engine, said torque converter further including a turbineand said lockup clutch further having an input member receiving torquefrom said output element, said torsion damper being disposed between anoutput member of said clutch and said turbine and said torque capacityat least approximating an upper limit of a first range of a plurality ofranges of torque being transmitted by said engine, said engine having amain driving range and at least a major part of said first range oftorques being transmitted within said main driving range.
 31. Apparatusfor transmitting torque from a rotary output element of an engine,comprising a hydrokinetic torque converter including a turbine, a lockupclutch having an input member receiving torque from said output element,and a torsional damper between an output member of said clutch and saidturbine, said damper having a torque capacity at least approximating anupper limit of a first range of a plurality of ranges of torque beingtransmittable by the engine, said first range of torques beingtransmitted while the engine is driven within an engine RPM rangebetween idling RPM and about 3000 RPM.
 32. The apparatus of claimwherein said first range of torques is being transmitted within anengine RPM range between idling RPM and 2000-2500 RPM.
 33. Apparatus fortransmitting torque from a rotary output element of an engine,comprising a hydrokinetic torque converter including a turbine, a lockupclutch having an input member receiving torque from said output element,and a torsional damper between an output member of said clutch and saidturbine, said damper having a torque capacity at least approximating anupper limit of a first range of a plurality of ranges of torque beingtransmittable by the engine, said plurality of ranges further embracinga second range of torques transmittable by the engine and the torquetransmitting capacity of said clutch within said second range beingbetween about 0.6 and 0.99 times the actual torque being transmitted bythe output element of the engine.
 34. The apparatus of claim 33, whereinthe torque transmitting capacity of said clutch within said second rangeis between 0.8 and 0.9 times the actual torque being transmitted by theoutput element of the engine.